High efficiency printing system for improved image quality

ABSTRACT

A high efficiency thermal printing system, comprising: a donor ribbon having donor material; a receiver medium; a test pattern to be printed on the receiver medium using the donor ribbon; a print head, a sensor, and a processor is disclosed. The present invention is adapted to print the test pattern on the receiver medium by heating the donor ribbon to cause the donor material to transfer from the donor ribbon onto the receiver medium, thereby depleting donor material on the donor ribbon. Moreover, the sensor is adapted to measure a depletion amount of the donor material on the donor ribbon after printing the test pattern, and the processor is adapted to calibrate the thermal printing system by adjusting a lookup table in response to the measured depletion amount of donor material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/829,534, filed May 31, 2013, and U.S. Provisional Application No.61/829,540, filed May 31, 2013. Furthermore, this application herebyincorporates by reference both U.S. Provisional Application Nos.61/829,534 and 61/829,540 in their entirety.

FIELD OF THE INVENTION

This invention pertains to the field of thermal printing systems andmore particularly to a method and system for calibrating thermalprinters that provides for improved image quality using high efficiencydonor ribbons and receivers. The method and system can also be used todetect when non high efficiency donor ribbons and receivers are loadedinto the thermal printer.

BACKGROUND OF THE INVENTION

In thermal dye sublimation printing, it is generally well known torender images by heating and pressing one or more donor materials suchas a colorant (e.g., a dye) or other coating against a receiver mediumhaving a colorant receiving layer. The heat is generally supplied by athermal print head having an array of modulated heating elements. Thedonor materials are typically provided in sized donor patches on amovable web known as a donor ribbon. The donor patches are organized onthe ribbon into donor sets; each set containing all of the donor patchesthat are to be used to record an image on the receiver web. For fullcolor images, multiple color dye patches can be used, such as yellow,magenta, and cyan donor dye patches. Arrangements of other color patchescan be used in like fashion within a donor set. Additionally, each donorset can include an overcoat or sealant layer.

Thermal printers offer a wide range of advantages in photographicprinting including the provision of truly continuous tone scalevariation and the ability to deposit, as a part of the printing processa protective overcoat layer to protect the images formed thereby frommechanical and environmental damage and fading. Accordingly, manyphotographic kiosks, portable printers, and home photo printerscurrently use thermal printing technology.

For low volume printing applications, such as portable or home thermalprinting systems, these types of printers are adapted to print onindividual sheets of receiver media. Thermal printing systems that areused for large volume applications, such as photographic kiosks,commonly utilize roll-fed receiver media.

Some current thermal printers utilize high efficiency donor ribbons andreceivers, where small amounts of transferable dye remains on thetransferable dye ribbon patch when printing high densities. Highefficiency donors have enough dye to create satisfactory D-max densitieson designated high efficiency receivers at a reduced level of thermalenergy. These printers use a reduced amount of energy provided by thethermal print head to transfer the proper amount of dye to produce thecorrect maximum density color image. Printing methods and systems thatutilize high efficiency donor ribbons and receivers use less energy andproduce less heat, which reduces environmental impacts, energyconsumption, and extends the operating life of the print head. Usingstandard thermal donor ribbons and receivers in a printing systemdesigned to utilize high efficiency donor ribbons and receivers cancause premature wear and damage to the print head. These conditions canbe caused by running the print head hotter than intended. Standard donorribbons tend to be more abrasive than high efficiency donor ribbonscausing premature wear. Using standard donor ribbons and receivers inprinting systems designed to use high efficiency donor ribbons andreceivers also causes reduction in image quality and requiresre-calibration of the printer to compensate for this media type in orderto produce an acceptable print.

In addition, requiring less energy to make high quality thermal printsnot only reduces energy costs, it also enhances applications such asportability for on-site event imaging, stand alone and user operatedretail kiosks, and home printing. These applications also make itdifficult to calibrate the printer since a procedure must be performedby a knowledgeable user or trained operator that also requires ascanner, densitometer, or spectrophotometer to read a printedcalibration target. The calibration target readings have to be enteredback into the printer or a computer connected to the printer in orderfor the printer to be calibrated. Printer calibration is beneficial whenreplacing expended donor ribbons and receivers to compensate formanufacturing lot variations in media and or changes in ambientconditions, such as transporting the printer from and indoor to outdoorvenue. However, typical calibration procedures waste time, materials,and require expensive ancillary equipment.

Some thermal printing systems incorporate optical emitters and sensorswhich are used to measure and analyze the color and density of thermaldonor ribbon patches to determine that the correct donor ribbon patchcolor is in position in order to print the appropriate cyan, magenta,yellow color image layer and protective clear overcoat layer.

There remains a need in the art for a method to calibrate a highefficiency thermal printing system for printing color images which usesa thermal printer having high efficiency dye donor ribbon, having arepeating series of spaced patches of yellow, magenta and cyan coloredheat transferable dyes and a protective clear overcoat layer, on to ahigh efficiency dye receiving sheet.

SUMMARY OF THE INVENTION

The present invention is directed to a system for calibrating a thermalprinter by adjusting a look up table, comprising: a donor ribbon havingdonor material, a print head located in the thermal printer, wherein theprint head is adapted to print images by transferring donor materialfrom the donor ribbon onto a receiver medium, and a test pattern to beprinted on the receiver medium. The system is further adapted to printthe test pattern on the receiver medium by heating the print head toheat the donor ribbon causing the donor material to transfer from thedonor ribbon onto the receiver medium, thereby depleting donor materialon the donor ribbon. A further design of the system includes a sensoradapted to measure a depletion amount of the donor material on the donorribbon after printing, and a processor adapted to adjust the lookuptable based on the measured depletion amount of donor material, therebycalibrating the thermal printer. In another embodiment, the presentinvention is directed to a system for detecting incorrect media in athermal printer comprising a sensor adapted to measure a depletionamount of donor material and a processor that is adapted to measure thedepletion amount of donor material and to detect whether the depletionamount is different from the expected depletion amount by a particularthreshold.

Advantages of the present invention include use of less energy andproduction of less heat, which reduces environmental impacts, energyconsumption, and extends the operating life of the print head. Anotheradvantage of the present invention is that it provides a calibrationmethod for a high efficiency thermal printing system for printing colorimages which uses a thermal printer having high efficiency dye donorribbon, having a repeating series of spaced patches of yellow, magentaand cyan colored heat transferable dyes and a protective clear overcoatlayer, on to a high efficiency dye receiving sheet.

The outer wrap of a new roll of receiver or the top sheet of a cut sheetstack is typically discarded due to potential artifacts from fingerprints and abrasions from handling and loading a roll or sheet stackinto the printer. This section of receiver is adequate to be used toprint the test target and as a result not be wasted. The existingoptical emitters and sensors are used to determine that the appropriatecolor patch in the repeating sequence is in the proper position and havebeen adapted for to perform routine printer calibration. Embedded highefficiency printing logic and the existing sensors and emitters are usedfor identifying the different color patches of each series of spacedpatches, to provide a method to measure a depletion amount of the donormaterial on the donor ribbon after printing the test pattern. Aprocessor is used to adjust the lookup table based on the measureddepletion amount of donor material, thereby calibrating the thermalprinter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a system diagram for an exemplary thermal printing system;

FIG. 2 is a diagram showing a bottom view of a thermal printhead;

FIG. 3A is a diagram illustrating a donor ribbon having four differentdonor patches;

FIGS. 3B-3C illustrate a printing operation;

FIG. 4 shows an example of a test pattern to be printed on the receivermedium;

FIG. 5A shows an embodiment of the configuration of an emitter anddetector pair according to an aspect of the present invention;

FIG. 5B shows another embodiment of the configuration of an emitter anddetector pair according to an aspect of the present invention;

FIG. 6A shows another embodiment of the configuration of an emitter anddetector pair according to an aspect of the present invention;

FIG. 6B shows another embodiment of the configuration of an emitter anddetector pair according to an aspect of the present invention;

FIG. 7 shows a flowchart for a method for calibrating a thermal printeraccording to an aspect of the present invention; and

FIG. 8 shows a flowchart for a method for detecting incorrect media in athermal printer according to an aspect of the present invention.

It is to be understood that the attached drawings are for purposes ofillustrating the concepts of the invention and may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system diagram for an exemplary thermal printer 18 inaccordance with the present invention. As shown in FIG. 1, thermalprinter 18 has a printer controller 20 that causes a thermal print head22 to record images onto receiver media 26 by applying heat and pressureto transfer material from a donor ribbon 30 to receiver media 26. Thereceiver media 26 includes a dye receiving layer coated on a substrate.As used herein, the term “receiver medium” and “receiver media” is usedsynonymously with the terms “thermal imaging receiver” and “thermalmedia.” Similarly, the term “donor ribbon” is used synonymously with theterms “thermal donor” and “donor web.”

Printer controller 20 can include, but is not limited to: a programmabledigital computer, a programmable microprocessor, a programmable logiccontroller, a series of electronic circuits, a series of electroniccircuits reduced to the form of an integrated circuit, or a series ofdiscrete components. According to an aspect of the invention shown inFIG. 1, printer controller 20 also controls receiver supply pick rollers41, a receiver drive roller 42, receiver exit rollers 43, a donor ribbontake-up roll 48, and a donor ribbon supply roll 50; which are eachmotorized for rotation on command of the printer controller 20 to effectmovement of receiver medium 26 and donor ribbon 30.

FIG. 2 shows a bottom view according to one aspect of a typical thermalprint head 22 with an array of thermal resistors 43 fabricated in aceramic substrate 45. A heat sink 47, typically in the form of analuminum backing plate, is fixed to a side of the ceramic substrate 45.Heat sink 47 rapidly dissipates heat generated by the thermal resistors43 during printing. As shown in FIG. 2, the thermal resistors 43 arearranged in a linear array extending across the width of platen roller46 (shown in phantom). Such a linear arrangement of thermal resistors 43is commonly known as a heat line or print line. However, othernon-linear arrangements of thermal resistors 43 can be used in variousaspects of the present invention. Further, it will be appreciated thatthere are a wide variety of other arrangements of thermal resistors 43and thermal print heads 22 that can be used in conjunction with thepresent invention.

The thermal resistors 43 are adapted to generate heat in proportion toan amount of electrical energy that passes through thermal resistors 43.During printing, printer controller 20 transmits signals to a circuitboard (not shown) to which thermal resistors 43 are connected, causingdifferent amounts of electrical energy to be applied to thermalresistors 43 so as to selectively heat donor ribbon 30 in a manner thatis intended to cause donor material to be applied to receiver medium 26in a desired manner.

As is shown in FIG. 3A, donor ribbon 30 comprises a first donor patchset 32.1 having a yellow donor patch 34.1, a magenta donor patch 36.1, acyan donor patch 38.1 and a clear donor patch 40.1; and a second donorpatch set 32.2 having a yellow donor patch 34.2, a magenta donor patch36.2, a cyan donor patch 38.2 and a clear donor patch 40.2. Each donorpatch set 32.1 and 32.2 has a patch set leading edge L and a patch settrailing edge T. In order to provide a full color image with a clearprotective coating, the four patches of a donor patch set; are printed,in registration with each other, onto a common image receiving area 52of receiver medium 26 shown in FIG. 3B. The printer controller 20(FIG. 1) provides variable electrical signals in accordance with inputimage data to the thermal resistors 43 (FIG. 2) in the thermal printhead 22 in order to print an image onto the receiver media 26. Eachcolor is successively printed as the receiver medium 26 and the donorribbon move from right to left as seen by the viewer in FIG. 3B.

During printing, the printer controller 20 raises thermal print head 22and actuates donor ribbon supply roll 50 (FIG. 1) and donor ribbontake-up roll 48 (FIG. 1) to advance a leading edge L of the first donorpatch set 32.1 to the thermal print head 22. In the embodimentillustrated in FIGS. 3A-3C, leading edge L for first donor patch set32.1 is the leading edge of yellow donor patch 34.1. As will bediscussed in greater detail below, the position of this leading edge Lcan be determined by using a position sensor to detect an appropriatemarking indicia on donor ribbon 30 that has a known position relative tothe leading edge of yellow donor patch 34.1 or by directly detecting theleading edge of yellow donor patch 34.1.

Printer controller 20 also actuates receiver pick rollers 41 (FIG. 1) topick cut sheet receiver from receiver supply cassette 44 (FIG. 1) intodrive roller 42 (FIG. 1). Printer controller 20 also actuates driveroller 42 (FIG. 1), so that image receiving area 52 of receiver medium26 is positioned with respect to the thermal print head 22. In theembodiment illustrated, image receiving area 52 is defined by areceiving area leading edge LER and a receiving area trailing edge TERon receiver media 26. Donor ribbon 30 and receiver media 26 arepositioned so that donor patch leading edge LED of yellow donor patch34.1 is registered at thermal print head 22 with receiving area leadingedge LER of image receiving area 52. Printer controller 20 then causes amotor or other conventional structure (not shown) to lower thermal printhead 22 so that a lower surface of donor ribbon 30 engages receivermedium 26 which is supported by platen roller 46. This creates apressure holding donor ribbon 30 against receiver media 26.

Printer controller 20 then actuates receiver drive roller 42 (FIG. 1),donor ribbon take-up roll 48 (FIG. 1), and donor ribbon supply roll 50(FIG. 1) to move receiver medium 26 and donor ribbon 30 together pastthe thermal print head 22. Concurrently, printer controller 20selectively operates thermal resistors 43 (FIG. 2) in thermal print head22 to transfer donor material from yellow donor patch 34.1 to receivermedia 26.

As donor ribbon 30 and receiver medium 26 leave the thermal print head22, a peel member 54 (FIG. 1) separates donor ribbon 30 from receivermedium 26. Donor ribbon 30 continues over idler roller 56 (FIG. 1)toward the donor ribbon take-up roll 48. As shown in FIG. 3C, printingcontinues until the receiving area trailing edge TER of image receivingarea 52 of receiver medium 26 reaches the printing zone between thethermal print head 22 and the platen roller 46. The printer controller20 then adjusts the position of donor ribbon 30 and receiver medium 26using a predefined pattern of movements so that a leading edge of eachof the next donor patches (i.e., magenta donor patch 36.1) in the firstdonor patch set 32.1 are brought into alignment with receiving arealeading edge LER of image receiving area 52 and the printing process isrepeated to transfer further material to the image receiving area 52.This process is repeated for each donor patch thereby forming thecomplete image.

Returning to a discussion of FIG. 1, the printer controller 20 operatesthe thermal printer 18 based upon input signals from a user input system62, an output system 64, a memory 68, a communication system 74, andsensor system 80. The user input system 62 can comprise any form oftransducer or other device capable of receiving an input from a user andconverting this input into a form that can be used by printer controller20. For example, user input system 62 can comprise a touch screen input,a touch pad input, a 4-way switch, a 6-way switch, an 8-way switch, astylus system, a trackball system, a joystick system, a voicerecognition system, a gesture recognition system or other such userinput systems. An output system 64, such as a display or a speaker, isoptionally provided and can be used by printer controller 20 to providehuman perceptible signals (e.g., visual or audio signals) for feedback,informational or other purposes.

Data including, but not limited to, control programs, digital images andmetadata can also be stored in memory 68. Memory 68 can take many formsand can include without limitation conventional memory devices includingsolid state, magnetic, optical or other data storage devices. In FIG. 1,memory 68 is shown having a removable memory interface 71 forcommunicating with removable memory (not shown) such as a magnetic,optical or magnetic disks. The memory 68 is also shown having a harddrive 72 that is fixed with thermal printer 18 and a remote memory 76that is external to printer controller 20 such as a personal computer,computer network or other imaging system.

As shown in FIG. 1, printer controller 20 interfaces with acommunication system 74 for communicating external devices such asremote memory 76. The communication system 74 can include for example, awired or wireless network interface that can be used to receive digitalimage data and other information and instructions from a host computeror network (not shown).

A sensor system 80 includes circuits and systems that are adapted todetect conditions within thermal printer 18 and, optionally, in theenvironment surrounding thermal printer 18, and to convert thisinformation into a form that can be used by the printer controller 20 ingoverning printing operations. Sensor system 80 can take a wide varietyof forms depending on the type of media therein and the operatingenvironment in which thermal printer 18 is to be used.

As shown in FIG. 1, sensor system 80 includes an optional donor positionsensor 82 that is adapted to detect the position of donor ribbon 30, anda receiver position sensor 84 that is adapted to detect a position ofthe receiver medium 26. The printer controller 20 cooperates with donorposition sensor 82 to monitor the donor ribbon 30 during movementthereof so that the printer controller 20 can detect one or moreconditions on donor ribbon 30 that indicate a leading edge of a donorpatch set. In this regard, the donor ribbon 30 can be provided withmarkings or other optically, magnetically or electronically sensibleindicia between each donor patch set (e.g., donor patch set 32.1) orbetween donor patches (e.g., donor patches 34.1, 36.1, 38.1, and 40.1).Where such markings or indicia are provided, donor position sensor 82 isprovided to sense these markings or indicia, and to provide signals tocontroller 20. The printer controller 20 can use these markings andindicia to determine when the donor ribbon 30 is positioned with theleading edge of the donor patch set at thermal print head 22. In asimilar way, printer controller 20 can use signals from receiverposition sensor 84 to monitor the position of the receiver medium 26 toalign receiver medium 26 during printing. Receiver position sensor 84can be adapted to sense markings or other optically, magnetically orelectronically sensible indicia between each image receiving area ofreceiver media 26.

During a full image printing operation, the printer controller 20 causesdonor ribbon 30 to be advanced in a predetermined pattern of distancesso as to cause a leading edge of each of the donor patches (e.g., donorpatches 34.1, 36.1, 38.1, and 40.1) to be properly positioned relativeto the image receiving area 52 at the start each printing process. Theprinter controller 20 can optionally be adapted to achieve suchpositioning by precise control of the movement of donor ribbon 30 usinga stepper type motor for motorizing donor ribbon take-up roll 48 ordonor ribbon supply roll 50 or by using a movement sensor 86 that candetect movement of donor ribbon 30. In one example, a follower wheel 88is provided that engages donor ribbon 30 and moves therewith. Followerwheel 88 can have surface features that are optically, magnetically orelectronically sensed by the movement sensor 86. According to one aspectof the present invention, the follower wheel 88 that has markingsthereon indicative of an extent of movement of donor ribbon 30 and themovement sensor 86 includes a light sensor that can sense lightreflected by the markings. According to other aspects of the presentinvention, perforations, cutouts or other routine and detectable indiciacan be incorporated onto donor ribbon 30 in a manner that enables themovement sensor 86 to provide an indication of the extent of movement ofthe donor ribbon 30.

As is also illustrated in FIG. 1, printer 18 includes a color sensingsystem having a light source or emitter 102 and a detector 104. In oneembodiment, the emitter 102 is adapted to emit light of a particularcolor to a portion of donor ribbon 30. The emitted light can be whitelight, neutral light, or any of colored light such as red, green, orblue. In this embodiment, detector 104 can comprise an opto-electroniccircuit having a sensing surface (not shown) that can sense anon-absorbed portion of the light applied to donor ribbon 30 by emitter102 and that can generate a signal that is indicative of the color andintensity of the non-absorbed light. Examples of such a color sensingtype of detector 104 include, but are not limited to, a densitometer, acolor imager, a colorimeter or like device.

According to another aspect of the present invention, emitter 102 cancomprise a multi-color light source that can automatically, or inresponse to signals from printer controller 20, apply a pattern ofdifferently colored light to a portion of donor ribbon 30. Detector 104can be of a type that does not necessarily measure the color of thenon-absorbed portion of the light, but rather measures the intensity ofthe non-absorbed portion of the light using a plurality of lightsensors, each adapted to determine an intensity of light within aspecific range of frequencies and that provide signals indicativethereof to printer controller 20 so that printer controller 20 cancombine the signals to determine the color of the portion of donorribbon 30 being sensed thereby.

The color sensing system can sense light that is reflected by receivermedium 26 or it can sense light that is transmitted through donor ribbon30. FIG. 1 illustrates a transmitted light type of sensing wherein theemitter 102 is positioned to direct a light onto donor ribbon 30 andcolor light detector 104 is positioned to receive at least a portion ofthe light that is transmitted by the illuminated portion of donor ribbon30. The color sensing system operates in cooperation with printercontroller 20 and provides signals to printer controller 20 from whichprinter controller 20 can determine the colors sensed by color sensingsystem. Color sensing system can operate continuously, or can operateselectively, such as in response to signals from printer controller 20.

FIG. 4 shows an example of a test pattern to be printed on the receivermedium 26. The test pattern can include image portions at variousdifferent print densities to thermally transfer varying amounts of dyefrom the donor ribbon 30 to the receiver medium 26. In color printing,each color channel, Red, Green and Blue contains 8-bits of color, or24-bits total; Red 8-bits+Green 8-bits+Blue 8-bits. Each color channelcontains 256 shades of color. Each color image can contain 256 (R)×256(B)×256 (G), or more than 16 million different colors.

Commonly, these 256 shades for each color channel are associated with aCode Value (CV) that may be defined using hexadecimal notation (HEX) forthe combination of Red, Green and Blue color values (RGB). The lowestvalue that can be given is 0 (in HEX:00). The highest value that can begiven is 255 (in HEX:FF). The process to generate the correct codevalues is directly related to the amount of energy applied from thethermal print head 22 to transfer the yellow, magenta and cyan dyes tothe receiver medium 26. Code Value 0 results in the application of theamount of energy from the thermal print head 22 necessary to cause 0%dye transfer (while still maintaining print head temperature at aminimum desired level) for each color. Code Value 255 results in theapplication of the amount of energy from the thermal print head 22 tocause slightly less than 100% dye transfer for each color. There is asmall amount of energy held back for a margin of safety.

For common color printing, pre-determined energy values are applied fromthe thermal print head 22 for each RGB code value on each color patch,yellow, magenta and cyan to create the correct image quality. For ahighly efficient printing system, transfer of yellow, magenta or cyandye from the donor ribbon 30 to the receiver medium 26 should occur withthe lowest amount of energy possible. To verify that the pre-definedhigh efficient energy levels that are built into the printer's firmwarematch the high efficiency of the transferable donor ribbon 30 andreceiver medium 26, the transmitted or reflected light is measured pre-and post-depletion of the donor ribbon. In some aspects of the presentinvention, a first measurement can be made before the test pattern isprinted on the received medium 26 by measuring the amount of light thatpasses through, or is reflected by, a donor patch. A similar measurementis made after the test pattern 28 has been printed on the receivermedium 26. The target depletion of the dye on the donor ribbon 30 isbetween 0% and 100% based on the test pattern 28.

When the printer's pre-defined maximum dye transfer energy (CV255=Dmax)is applied, equal to or slightly less than 100% of the dye in thatportion of donor patch in a high efficiency donor ribbon 30 is depleted.When the printer's pre-defined near maximum dye transfer energy(CV228=D<max) has been applied, equal to or less than 90% of the dye inthat portion of donor patch has been depleted. When the printer'spre-defined mid level dye transfer energy (CV127=Dmid) has been applied,equal to or near 50% of the dye in that portion of donor patch has beendepleted. When the printer's pre-defined near minimum dye transferenergy (CV25=D>min) has been applied, equal to or less than 10% of thedye in that portion of donor patch has been depleted. When the printer'spre-defined minimum dye transfer energy (CV0=Dmin) has been applied,equal to or near 0% of the dye in that portion of donor patch has beendepleted.

If the printer's pre-defined near maximum dye transfer energy(CV228=D<max) has been applied, and near 100% of the dye in that portionof donor patch has been depleted, the high efficiency printing system isnot working properly. This means that the print output between CV228 upto CV255 does not show any difference. Similarly, if the printer'spre-defined near minimum dye transfer energy (CV25=D>min) has beenapplied, and 0% of the dye in that portion of donor patch has beendepleted, the high efficiency printing system is not working properly.This means that the print output between CV0 and CV25 does not show anydifference. The amount of energy required to affect dye transfercorresponding to particular code values can be stored in processoraccessible memory as a lookup table.

It should be noted that, in other aspects of the present invention, Dmaxcan be represented using CV0 and Dmin can be represented using CV255.The choice of code values used to represent the amount of energy neededto transfer a particular amount of dye from donor ribbon 30 ontoreceiver medium 26 can vary from system to system.

Incorporated herein by reference, U.S. Pat. No. 8,035,671B2 Dual-usesensor assembly for a thermal printer, filed Nov. 24, 2008 in the nameof Stuart Gerard Evans discloses using an embedded reflectiondensitometer for the purposes of neutral or color calibration inaddition to identifying the proper donor patch. The reflectiondensitometer or its equivalent is used to take reflection densitymeasurements from the surface of the printed media. In addition, thespecifications for the embedded densitometer are more stringent than forthe donor patch sensor assembly and requires a tone scale test targethaving a plurality of discrete patches ranging from low density to highdensity.

Incorporated herein by reference, U.S. Pat. No. 7,324,124 B2 Printer andmethod for detecting donor material, filed Nov. 18, 2005 in the names ofWalter H. Isaac, et al. discloses a method for operating a printer thatapplies donor material from donor patches on a donor ribbon to areceiver medium, the donor patches being organized into sets each setincluding at least one colored donor material patch and a protectivematerial donor patch, the method comprising the steps of: applying anon-visible light to a location on the donor ribbon; sensing a portionof non-visible light that is not absorbed by the donor ribbon; anddetermining whether the portion of the donor patch to which thenon-visible light has been applied has unused protective donor materialthereon, said determining being based upon the sensed non-visible light.

Incorporated herein by reference, U.S. Pat. No. 7,666,815B2 Thermaldonor for high-speed printing discloses a dye-donor element, a method ofprinting using the dye-donor element, and a print assembly including thedye-donor element, wherein the dye-donor layer of the dye-donor elementincludes ethyl cellulose as a binder. The dye-donor element is capableof printing a defect-free image on a receiver element at a line speed of2.0 msec/line or less while maintaining a print density of at least 2.0.

At high printing speeds, considered to be 2.0 msec/line or less, theprint head 22 undergoes heat on/off cycles very rapidly. This generatedheat must be driven through the dye-donor support assemblage veryrapidly to effect the dye transfer from the donor ribbon 30 to thereceiver medium 26. Each layer in the donor ribbon 30 can act as aninsulator, slowing down the heat transfer through the layers of thedonor ribbon 30 to the receiver medium 26. Because of the short heatapplication time, any reduction in heat transfer efficiency results in alower effective temperature in the donor layer during printing, whichcan result in a lower transferred dye density. It is known to overcomethe low print density associated with shorter line times by increasingthe printhead voltage, increasing the dye density in the dye-donorlayer, or a combination thereof. Applying higher print head voltages candecrease the lifetime of the thermal print head 22, requires a higherpower supply, and can require additional cooling delays, all of whichincrease cost. Increasing the dye density in the dye-donor layer alsoincreases costs, as well as increasing the chance of unwanted dyetransfer, such as during storage of a dye-donor element.

Another problem exists with many of the donor ribbons 30 and receivermedia 26 used in thermal dye transfer systems. At the high temperaturesused for thermal dye transfer, many polymers used in these elements cansoften and adhere to each other, resulting in sticking and tearing ofthe donor ribbon 30 and receiver media 26 upon separation from oneanother after printing. Areas of the dye-donor layer other than thetransferred dye can adhere to the receiver medium 26, causing printdefects ranging from microscopic spots to sticking of the entiredye-donor layer on the receiver medium 26. This is aggravated whenhigher printing voltages, resulting in higher temperatures, are used inhigh speed printing. Another problem with high speed printing is thatthe more rapid physical motion of the donor/receiver assembly results inhigher peel rates between the donor ribbon 30 and the receiver medium 26as they are separated after printing, which can aggravate sticking ofthe donor ribbon 30 and receiver medium 26.

FIG. 5A shows a configuration of an emitter and detector pair accordingto an aspect of the present invention. In the configuration shown inFIG. 5A, the emitter 102 is positioned above the donor ribbon 30 and thereceiver medium 26. The detector 104 is placed below the donor ribbon 30and the receiver medium 26. The signal emitted by the emitter 102 passesthrough both the donor ribbon 30 and the receiver medium 26 before beingdetected at the detector 104.

FIG. 5B shows a configuration of an emitter and detector pair accordingto another aspect of the present invention. In the configuration shownin FIG. 5B, the emitter 102 is positioned above the donor ribbon 30. Thereceiver medium 26 is moved out of the emitter detector path. Thedetector 104 is placed below the donor ribbon 30. The signal emitted bythe emitter 102 passes through the donor ribbon 30 before being detectedat the detector 104.

FIG. 6A shows a configuration of an emitter and detector pair accordingto another aspect of the present invention. In the configuration shownin FIG. 5B, both the emitter 102 and the detector 104 are positionedabove the donor ribbon 30. The receiver medium 26 is moved out of thesignal path. A reflective surface 106 is placed below the donor ribbon30. The signal emitted by the emitter 102 passes through the donorribbon 30, is reflected by the reflective surface 106, before beingdetected at the detector 104.

FIG. 6B shows a configuration of an emitter and detector pair accordingto another aspect of the present invention. In the configuration shownin FIG. 5B, both the emitter 102 and the detector 104 are positionedabove the donor ribbon 30 and the receiver medium 26. A reflectivesurface 106 is placed below the donor ribbon 30 and the receiver medium26. The signal emitted by the emitter 102 passes through the donorribbon 30 and the receiver medium 26, can be reflected by the receivermedium 26 or the reflective surface 106, before being detected at thedetector 104.

Different configurations of the emitter detector pair and the locationof the donor ribbon 30 and the receiver medium 26 allow for differentoperations to be performed on the printer. If both the donor ribbon 30and the receiver medium 26 are present in the emitter detector path, thedonor patch color can be read before printing the test pattern and thedonor depletion level can be measured after printing the test pattern tocalibrate the printer. The measured donor depletion level indicatesproper donor ribbon 30 and receiver medium 26 are loaded. The receivermedium 26 can be determined by moving the donor ribbon 26 to a clearlaminate patch and measuring the signal either transmitted through orreflected by the unprinted receiver medium 26 to determine receivertype. The receiver medium 26 can be moved out of emitter detector pathto measure the donor patch color on the donor ribbon in the emitterdetector path. The receiver medium 26 can then be moved back into theemitter detector path and a test pattern can be printed using the donorpatch. The receiver medium 26 can be moved out of the emitter detectorpath to measure the donor depletion level to calibrate the printer.

In another aspect of the present invention, wherein the emitter 102 anddetector 104 are both located above the donor ribbon 30, the receivermedium 26 can act as a reflector to reflect the signal off of theunprinted receiver medium 26. In another aspect of the presentinvention, a reflective surface 106, can be used to reflect the signalfrom the emitter 102 to the detector 104.

The color sensing system can also extend across a full printable widthof receiver medium 26 so that the color of any portion of image can besensed without translating color sensing system 60 relative to receivermedium 26.

Emitters 102 and detectors 104 can be selected to operate in the visibleor invisible range of the electromagnetic spectrum. These components canbe constructed as a single emitter and detector pair with a broadfrequency range or individual unit pairs to cover portions of thefrequency range. The chosen component configuration and frequencyresponse is sufficient to measure the color and density range of bothunused and depleted donor patch for each color of the donor patches,including black and metallic colored patches such as gold and silver.The frequency response range of the emitter and detector pair can alsobe selected to measure the reflective and or transmissive colors anddensities of unused and printed receiver media included various surfacetextures. The emitter and detector pair can also be configured tooperate in a transmissive or reflective mode. Receiver medium 26 can bemoved into and out of the optical path between emitter 102 and thedetector 104 by winding it back onto the roll for roll fed thermalprinters. For sheet fed thermal printers, the individual sheet would notbe fed into the optical path between the emitter 102 and the detector104 until required. The emitter and detector pair also identifies whichdonor patch in the repeating sequence of donor patches is in positionand can selectively place the clear laminate patch in the optical patchto read though the clear laminate patch in order to measure the color,density, or surface type of the receiver media, either by reflective ortransmissive configurations. Operationally the emitter and detector pairmeasure the donor patch depletion either directly from the donor patchor the amount of donor deposited on the receiver media.

In configurations where the emitter and detector pair are side by sideand operate in a mode that requires the light from the emitter to bereflected back to the detector, the light from the emitter passesthrough the selected donor patch and reflects off of either the surfaceof unused or printed receiver media or off of a reflective surface belowthe receiver media path, when the receiver media is out of the emitterdetector optical path. The reflective surface is an optical componentsuch as a front surface mirror or polished metallic or glass surface.

FIG. 7 shows a flowchart for a method for calibrating a thermal printeraccording to an aspect of the present invention. The thermal printer hasan Operator Control Panel called an OCP that displays various statusmessages. The printer power is turned on to activate the OCP display.The donor ribbon 30 and receiver medium 26 are loaded into the thermalprinter to stage the receiver medium 26 for printing a test pattern. TheOCP displays the corresponding messages based on the status of theprinter. The print head can be used to print the test pattern on thereceiver medium 26, which can then be ejected from the emitter detectorpath. The printer can optionally rewind the spent ribbon onto the supplyspool. The emitter detector pair can be used to measure a donordepletion level for one or more dye color patches. In a typical thermalprinter, a donor ribbon 30 may include yellow, magenta, cyan, and cleardonor dye patches. Based on the measured donor depletion levels,adjustments can be made to the lookup tables for the various color dyepatches to calibrate the printer for the donor ribbon 30. In otheraspects of the present invention, the adjustments can be stored as anadjustment table in processor accessible memory instead of directlychanging the lookup tables. The adjustment table can be linked to thelookup table to provide updated energy levels for high efficiencyprinting.

FIG. 8 shows a flowchart for a method for detecting incorrect media in athermal printer according to an aspect of the present invention. Thethermal printer has an Operator Control Panel called an OCP thatdisplays various status messages. The OCP display shows that the thermalprinter is ready for operation. The print head can be used to print thetest pattern on the receiver medium, which can then be ejected from theemitter detector path. The printer can optionally rewind the spentribbon onto the supply spool. The emitter detector pair can be used tomeasure a donor depletion level for one or more dye color patches andcompared with an expected donor depletion level. In a typical thermalprinter, a donor ribbon 30 may include yellow, magenta, cyan, and cleardonor dye patches. Where high efficiency printing is desired, thismethod can be used to determine the presence of a non high efficiencydonor ribbon 30 in the thermal printer and a warning message can bedisplayed on the OCP. In this case, the measured donor depletion levelis compared to the expected donor depletion level for a high efficiencydonor ribbon to determine whether the correct donor ribbon is loadedinto the thermal printer. Different threshold amounts, such as upto 5%or upto 10% difference between the expected and measured donor depletionlevels can be used for this comparison. The expected donor depletionlevel for a high efficiency donor ribbon 30 can be measured using themethod of FIG. 7 and stored in processor accessible memory for futureuse.

An aspect of the present invention includes a method and system forcalibrating a thermal printer by adjusting a look up table, comprising:providing a donor ribbon having donor material; providing a print headlocated in the thermal printer, the print head adapted to print imagesby transferring donor material from the donor ribbon onto a receivermedium; receiving a test pattern to be printed on the receiver medium;printing the test pattern on the receiver medium by heating the printhead to heat the donor ribbon causing the donor material to transferfrom the donor ribbon onto the receiver medium, thereby depleting donormaterial on the donor ribbon; using a sensor to measure a depletionamount of the donor material on the donor ribbon after printing; andusing a processor to adjust the lookup table based on the measureddepletion amount of donor material, thereby calibrating the thermalprinter.

The color of the donor material on the donor ribbon can include yellow,magenta, cyan, red, green, blue, gray, black, gold or silver orcombinations thereof. The donor ribbon can include a plurality ofcolored patches of donor material, the color of the patches includingmagenta, cyan, yellow, red, green, blue, gray, black, gold or silver orcombinations thereof.

The test pattern includes at least two portions with different codevalues, the different code values causing different amounts of donormaterial to be transferred from the donor ribbon onto the receivermedium, thereby depleting different amounts of donor material on thedonor ribbon. The first code value in the test pattern causes the printhead to transfer about 0% or about 100% of the donor material onto thereceiver medium and a second code value causes the print head totransfer between 5% and 95% of the donor material onto the receivermedium. The difference between the amount of depletion of donor materialat the first and second code values can be used to compute an adjustmentfor the lookup table.

The method and system described above can further include using thesensor to measure an initial amount of donor material on the donorribbon prior to depletion; and using the processor, when it adjusts thelookup table, to use the difference between the initial amount of donormaterial and the depletion amount of donor material to compute theadjustment.

The sensor can be an optical sensor comprising an emitter and detectorpair, further including emitting light of a particular wavelength fromthe emitter onto the used donor ribbon, transmitting or reflecting thelight from the used donor ribbon onto the detector, and measuring aresponse of the transmitted or reflected light from the detector. Thesensor can be a tri-color sensor with red, green and blue light emittersand corresponding detectors.

Another aspect of the present invention includes a method and system forcalibrating a thermal printer by adjusting a plurality of lookup tables,comprising: providing a plurality of donor ribbons having donormaterial, each donor ribbon being associated with a particular lookuptable; and using the method described above for each donor ribbon toadjust its associated lookup table, thereby calibrating the thermalprinter.

Another aspect of the present invention includes a method and system fordetecting incorrect media in a thermal printer, comprising, providing adonor ribbon having donor material, providing a print head located inthe thermal printer, the print head adapted to print images bytransferring donor material from the donor ribbon onto a receivermedium, receiving a test pattern to be printed on the receiver medium,printing the test pattern on the receiver medium by heating the printhead to heat the donor ribbon causing the donor material to transferfrom the donor ribbon onto the receiver medium, thereby depleting donormaterial on the donor ribbon, using a sensor to measure a depletionamount of the donor material on the donor ribbon after printing, andusing a processor to compare the measured depletion amount of donormaterial with an expected depletion amount of the donor material,thereby detecting incorrect media in the thermal printer when themeasured depletion amount of donor material is different from theexpected depletion amount by a particular threshold.

The invention is inclusive of combinations of the aspects of the presentinvention described herein. References to “a particular aspect” and thelike refer to features that are present in at least one aspect of theinvention. Separate references to “an aspect” or “particular aspects” orthe like do not necessarily refer to the same aspect or aspects;however, such aspects are not mutually exclusive, unless so indicated oras are readily apparent to one of skill in the art. The use of singularor plural in referring to the “method” or “methods” and the like is notlimiting. It should be noted that, unless otherwise explicitly noted orrequired by context, the word “or” is used in this disclosure in anon-exclusive sense.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

The invention claimed is:
 1. A high efficiency thermal printing system,comprising: a donor ribbon having donor material; a receiver medium; atest pattern to be printed on the receiver medium using the donorribbon, wherein the test pattern includes at least two portions withdifferent code values, whereby the different code values cause differentamounts of donor material to be transferred from the donor ribbon ontothe receiver medium; a print head located in a thermal printer, whereinthe print head is adapted to print the test pattern on the receivermedium by heating the donor ribbon to cause the donor material totransfer from the donor ribbon onto the receiver medium, therebydepleting donor material on the donor ribbon; a sensor adapted tomeasure a depletion amount of the donor material on the donor ribbonafter printing the test pattern; and a processor adapted to calibratethe thermal printing system by adjusting a lookup table in response tothe measured depletion amount of donor material.
 2. The thermal printingsystem of claim 1 wherein the color of the donor material on the donorribbon includes yellow, magenta, cyan, red, green, blue, gray, black,gold or silver or combinations thereof.
 3. The thermal printing systemof claim 1 wherein the donor ribbon further includes a plurality ofcolored patches of donor material, and the color of the patches ischosen from the group consisting of magenta, cyan, yellow, red, green,blue, gray, black, gold or silver or combinations thereof.
 4. Thethermal printing system of claim 1 wherein the sensor is an opticalsensor comprising an emitter and detector pair adapted to emit light ofa particular wavelength from the emitter onto the used donor ribbon, totransmit or reflect the light from the used donor ribbon onto thedetector, and to measure a response of the transmitted or reflectedlight from the detector.
 5. The thermal printing system of claim 4wherein the sensor is a tri-color sensor with red, green, and blue lightemitters and corresponding detectors.
 6. The thermal printing system ofclaim 1 wherein a first code value associated with a first portion ofthe test pattern causes the print head to transfer about 0% or about100% of the donor material onto the receiver medium and a second codevalue associated with a second portion of the test pattern causes theprint head to transfer between 5% and 95% of the donor material onto thereceiver medium.
 7. The thermal printing system of claim 6 wherein thesensor measures a difference between the amount of depletion of donormaterial at the first and second code values to compute an adjustmentfor the lookup table.
 8. A high efficiency thermal printing systemcomprising: a donor ribbon having donor material; a receiver medium; atest pattern to be printed on the receiver medium using the donorribbon; a print head located in a thermal printer, wherein the printhead is adapted to print the test pattern on the receiver medium byheating the donor ribbon to cause the donor material to transfer fromthe donor ribbon onto the receiver medium, thereby depleting donormaterial on the donor ribbon; a sensor adapted to measure a depletionamount of the donor material on the donor ribbon after printing the testpattern; and a processor adapted to detect incorrect media in thethermal printer when the measured depletion amount of donor material isdifferent from an expected depletion amount by a particular threshold.9. The thermal printing system of claim 8 wherein the color of the donormaterial on the donor ribbon includes yellow, magenta, cyan, red, green,blue, gray, black, gold or silver or combinations thereof.
 10. Thethermal printing system of claim 8 wherein the donor ribbon furtherincludes a plurality of colored patches of donor material, the color ofthe patches including magenta, cyan, yellow, red, green, blue, gray,black, gold or silver or combinations thereof.
 11. The thermal printingsystem of claim 8 wherein the test pattern includes at least twoportions with different code values, whereby the different code valuescause different amounts of donor material to be transferred from thedonor ribbon onto the receiver medium.
 12. The thermal printing systemof claim 11 wherein a first code value associated with a first portionof the test pattern causes the print head to transfer about 0% or about100% of the donor material onto the receiver medium and a second codevalue associated with a second portion of the test pattern causes theprint head to transfer between 5% and 95% of the donor material onto thereceiver medium.
 13. The thermal printing system of claim 8 wherein thesensor is an optical sensor comprising an emitter and detector pair,further including emitting light of a particular wavelength from theemitter onto the used donor ribbon, transmitting or reflecting the lightfrom the used donor ribbon onto the detector, and measuring a responseof the transmitted or reflected light from the detector.
 14. The thermalprinting system of claim 13 wherein the sensor is a tricolor sensor withred, green, and blue light emitters and corresponding detectors.
 15. Thethermal printing system of claim 8 wherein the particular threshold isup to 5% difference between the measured amount of depletion and theexpected amount of depletion.
 16. The thermal printing system of claim 8wherein the particular threshold is up to 10% difference between themeasured amount of depletion and the expected amount of depletion.